Hydraulically actuatable gearshift system comprising a synchronizing device

ABSTRACT

A transmission shift system comprising a synchronizing device for idler wheels, which comprises one sliding sleeve that can mesh with a selected idler wheel. The sliding sleeve is arranged non-rotatably and axially displaceable on a shaft with hydraulic actuation being provided. Each sliding sleeve ( 6 ) is connected with the shaft ( 1 ) via a hub element ( 7 ). The synchronizing operation can be implemented as a function of the hydraulic actuation pressure.

The present invention relates to a transmission shift system comprising a synchronizing device for idler wheels pursuant to the preamble of patent claim 1.

From the state of the art is known of transmission shift systems for idler wheels. In the familiar transmission shift systems, generally, synchronizing devices are provided for the purpose of synchronizing the idler wheels, wherein the devices mechanically actuate the sliding sleeves in order to synchronize the desired idler wheel with a shaft. This way the necessary torque is transmitted from the idler wheel to the shaft or vice versa.

Generally, a displaceable sliding sleeve is used as the shifting element, having an appropriate profile, which slides onto the profile of the counter-piece upon actuation. For this, it is required that the normally existing RPM differential between the idler wheel and the shaft first assumes the value zero. Otherwise, it is not possible to connect the two profiles without resulting in undesirable grating in the transmission. Accordingly, the two profiles should only come into contact with each other when the rotational speeds between the idler wheel to be shifted and the shaft have been balanced. Therefore, a locking synchronizing device is provided, which prevents early shifting through a mechanical locking device.

The publication DE 37 11 490 C2 discloses a gear shifting device. In this gear shifting device, the sliding sleeve is actuated by an adjusting arrangement accommodated in the shaft and operated by means of hydraulic fluid, wherein the arrangement consists of a hydraulically actuatable piston arrangement. A connecting pin, which connects the sliding sleeve with the hydraulic piston arrangement, is provided, which extends through a hole with axial play that is arranged transversely in the shaft. The familiar gear shifting device disadvantageously requires a very complex layout, since the actuating device or piston arrangement is accommodated in the gear shaft. This affects the manufacturing costs of the familiar gear shifting devices negatively.

From the publication GB 2 214 248 A is known of a gear ratio selection mechanism for a motor vehicle transmission. The mechanism utilizes fluid-operated actuators and an electro-hydraulic driver. With a first actuator the desired gear ratio is selected and, with a second actuator, a movement in the direction of the neutral path is enabled, wherein the first actuator activates a desired gear ratio by moving transversely to the neutral path. Furthermore, potentiometers are provided, which allow the respective positions of the actuators to be determined and be passed on to a control system in the form of signals.

It is the object of the present invention to suggest a transmission shift system of the aforementioned kind, which comprises a synchronization device with a simple design of which easy and also secure synchronization can be achieved.

This objective is achieved pursuant to the invention through the features of patent claim 1. Further variations and advantages result from the dependent claims.

Accordingly, according to the invention, a transmission shift system with a synchronization device is suggested, in which a synchronizing operation is enabled during the shifting operation in a simple fashion. In particular, additional mechanical components of a locking device can be foregone in the transmission shift system according to the invention. By actuating the sliding sleeve hydraulically and by connecting the sliding sleeve with the shaft, via a hub element, the RPM adjustment of the idler wheel to be shifted and the shaft can be implemented in a simple manner. As a function of the actuation pressure, the sliding sleeve can be axially displaced in such a way that, initially, the existing rotational speed difference between the idler wheel and the shaft is compensated. After the rotational speed adjustment has occurred, the sliding sleeve can then be displaced axially in such a way that the sliding sleeve engages with the idler wheel to be shifted.

Within the framework of further developing the invention, a catch device can be provided for driving the axial movement of the sliding sleeve or of the hub element. The catch device can be a spring-ball element or the like. It can be provided that the hub element comprises a bore in the radial direction in which the spring-loaded ball of the spring-ball unit is guided. The ball is pushed into a groove provided in the sliding sleeve by the spring. Through the actuation pressure acting in the axial direction, the sliding sleeve can be moved in the axial direction. As a function of the amount of the actuation pressure, the catch device releases the sliding sleeve at a predetermined actuation pressure P_(S) so that it can mesh with the idler wheel once the same RPM exists for the idler wheel and the shaft. It is also conceivable that other mechanically or similarly operated catch devices are used for the transmission shift system according to the invention.

Preferably, the hydraulic actuation of the sliding sleeve is provided by an actuating piston or the like. Upon the piston pressure can be applied via an oil supply system so that the sliding sleeve is displaced axially in a corresponding fashion. It is also feasible that other actuating types are provided for the sliding sleeve.

According to a further beneficial development of the present invention, at least one disk, which is preferably designed as a brake plate, can be provided to adjust the RPMs between the idler wheel to be shifted and the shaft. Every brake plate comprises corresponding friction surfaces, which are preferably coated with a suitable material in order to enable RPM adjustment in the simplest manner.

The invention is explained in further detail in the following based on the attached figures. They show:

FIG. 1 is a cross-sectional partial view of a possible embodiment of a transmission shift system pursuant to the invention;

FIG. 2 is a possible course of the actuation pressure during the synchronizing process; and

FIG. 3 is a cross-sectional partial view of another embodiment of the transmission shift system pursuant to the invention.

FIG. 1 shows a possible embodiment of the transmission shift system according to the invention. The transmission shift system comprises a synchronizing device for idler wheels 2. At least one sliding sleeve 6, which can mesh with an idler wheel 2 that is to be shifted, is provided. The sliding sleeve 6 is arranged non-rotatably and axially displaceable on a shaft 1, wherein the sliding sleeve 6 can be hydraulically actuated by means of an actuating piston 10. The idler wheel 2 is arranged rotatably on the shaft 1 and meshes with additional torque-transmitting elements.

According to the invention, it is provided that the sliding sleeve 6 is connected with the shaft 1 via a hub element 7 wherein, as a function of the hydraulic actuation pressure, an existing RPM difference between the idler wheel 2 to be shifted and the shaft 1 is compensated. Accordingly the shaft 1 and the idler wheel 2 to be shifted are connected so as to transmit torque. This way, the synchronizing operation is achieved with minimal design effort and in the quickest possible fashion.

For the purpose of adjusting the RPMs during the synchronizing operation, the idler wheel 2 to be shifted is clamped between two disk elements 4, 5. The two disk elements 4, 5 are connected non-rotatably with the shaft 1 via profiles, wherein the disk elements 4, 5 each comprise a friction surface on the sides facing the idler wheel 2, said surfaces being suitably coated. The clamping force that is required for the synchronizing operation is applied hydraulically onto the sliding sleeve 6 by the actuating piston 10. The actuating piston 10 is returned into its starting position after synchronizing by means of a return spring 11.

For the purpose of driving the axial motion of the sliding sleeve 6, a suitable catch device is provided on the hub element 7. The catch device comprises, in the embodiment shown here, a so-called spring-ball unit, which is provided in a bore of the hub element 7. A ball 9 of said unit is pushed into a catch groove of the sliding sleeve 6 by a spring element 8.

The selected design of a catch groove 3 combined with the amount of the spring force determines the necessary axial displacement force that must be applied onto the sliding sleeve 6 before said sleeve can move out of the starting position.

If said force is lower than the release force, the sliding sleeve 6 remains locked in its position. Said force can, however, be used to apply a suitable clamping force onto the disk elements 4, 5. This way the disk elements 4, 5 are pressed against the idler wheel 2 to be shifted so that the RPM difference between the idler wheel 2 and the shaft 1 is compensated. Preferably at least the disk element 4 comprises a stop element 14 in the axial direction.

The ball 9 and the spring 8 are guided in a bore in the hub element 7, which is provided loosely displaceable in the axial direction on the shaft 1. The hub element 7 rests directly against the disk element 5. The disk element 5, like the hub element 7, is connected to the shaft 1, via a profile, in order to transmit the necessary torque from the sliding sleeve 6 onto the shaft 1 in the shifted state.

As soon as the force, acting upon the sliding sleeve 6 from the actuation pressure, exceeds the release force, the ball 9 can be pushed out of the groove 3 into the bore against the spring force of the spring element 8, so that the sliding sleeve 6 is axially displaced and can mesh with the idler wheel 2. When the ball 9 is located outside the catch groove 3, the clamping force, that is applied on the idler wheel 2, is also reduced to zero. This way, the corresponding meshing of the two splines of the idler wheel 2 and the sliding sleeve 6 can be beneficially facilitated.

When releasing the connection, the sliding sleeve 6 can be pulled into the opposite direction by the return spring 11 of the actuating piston 10. The ball 9 can reach the catch groove 3 of the sliding sleeve 6 and, this way, the hub element 7 is removed from the disk element 5. Accordingly, the clamping force can be completely eliminated from the idler wheel 2.

Accordingly, no additional mechanical locking device is required in the transmission shift system according to the invention. The synchronizing operation, provided with the transmission shift system, is essentially accomplished by applying pressure onto the actuating piston 10. The actuation pressure can preferably, as shown in FIG. 2, be adjusted in two steps. In the non-switched state, the actuation pressure can be equal to the pressure P₀ at the time t₀. The pressure P₀ is so low that no force counteracts the return spring 11 of the actuating piston 10.

During the start of a shifting operation, the actuation pressure is increased to its first step, i.e., to the pressure P₁. Through the pressure P₁ it is accomplished that the actuating piston 10 can be moved against the spring force of the return spring 11, wherein the excess force on the actuating piston 10 is then axially transmitted onto the sliding sleeve 6. The actuation pressure P₁, however, is not able to apply sufficient force onto the sliding sleeve 6 to displace it against the catch device.

This way the force is transmitted onto the disk element 5 via the ball 9 and the hub element 7. As long as the actuating pressure P₁ is applied, a corresponding clamping force acts upon the idler wheel 2, and the existing RPM difference between the idler wheel 2 and the shaft 1 is compensated. The time during which the application pressure P₁ is applied is the corresponding synchronizing time, which is specified by the time interval t_(1,2) in FIG. 2. It should be noted that said time is sufficiently great to enable a suitable speed adjustment. This can occur by measuring the respective rotational speed of the shaft 1 and of the idler wheel 2, whereby the synchronizing time t_(1,2) is determined then. It is also conceivable that the synchronizing time is known since it is known what state all rotating parts in the transmission are in, and the respectively required time for the synchronizing operation can be determined.

When the RPM adjustment has been made, the actuation pressure can be raised to the second step, i.e., to the pressure P₂. The actuation pressure P₂ is large enough to overcome the release forces on the catch device. This way the sliding sleeve 6 is axially displaced in such a way that it can mesh with the idler wheel 2. It should be noted that the actuation pressure P_(S), marked in FIG. 2, is the appropriate pressure at which the release takes place. The actuation pressure P_(S) here is between the two actuation pressures P_(S) and P₂. The amount of the distance from P_(S) to P₁, as well as the amount of the distance from P_(S) to P₂ must each be so large that all system tolerances of the transmission are taken into consideration.

The pressure course, illustrated in FIG. 2, is only provided by way of example so that other random application force progressions are also feasible with the transmission shift system according to the invention.

FIG. 3 shows another possible embodiment of the transmission shift system, according to the present invention, wherein identical components were marked with the same reference numerals as in FIG. 1.

The embodiment can be preferably used when greater torque is required to adjust the speed differential between the idler wheel 2 and the shaft 1. This is accomplished in that an additional brake plate 13 is provided in the axial direction between the hub element 7 and the disk element 5. This results in additional friction surfaces, thus being able to apply a greater brake torque onto the idler wheel 2 to be shifted. Preferably, the brake plate 13 has exterior splines, which engage with the same splines; the splines of the sliding sleeve 6 mesh with. Beneficially, this way the usable synchronizing torque doubles as well.

REFERENCE NUMERALS

-   1 shaft -   2 idler wheel -   3 catch groove -   4 disk element -   5 disk element -   6 sliding sleeve -   7 hub element -   8 spring element -   9 ball -   10 actuating piston -   11 return spring -   12 oil supply system -   13 brake plate -   14 stop element 

1-11. (canceled)
 12. A transmission shift system comprising a synchronizing device for idler wheels (2), which comprises at least one sliding sleeve that can mesh with a selected idler wheel, the sliding sleeve being arranged non-rotatably and axially displaceable on a shaft (1), with hydraulic actuation being provided, each of the at least one sliding sleeve (6) is connected with the shaft (1) via a hub element (7), a synchronizing operation can be implemented as a function of hydraulic actuation pressure, in a non-switched state the actuation pressure is equal to an initial pressure (P₀) at which no axial movement of the sliding sleeve (6) is possible, and for the purpose of releasing the sliding sleeve (6) the actuation pressure is raised to a second pressure (P_(S)), at which the sliding sleeve (6) can be axially displaced in such a way, that the sliding sleeve (6) and the idler wheel (2) can mesh with each other, for rpm adjustment purposes the actuation pressure is raised to a first pressure (P₁), which is greater than the actuation initial pressure (P₀) in a non-switched state and lower than the actuation second pressure used for release purposes (P_(S)), at the actuation first pressure (P₁) a slight axial displacement of the sliding sleeve (6) for the rpm adjustment is possible.
 13. The transmission shift system according to claim 12, wherein a time duration, at which the actuation first pressure (P₁) acts upon the hydraulic actuation for rotational speed adjustment purposes can be determined by means of direct or indirect measurement of the RPMs of the idler wheel (2) and the shaft (1).
 14. The transmission shift system according to claim 12, wherein the hub element (7) comprises a catch device, which enables an axial movement of the sliding sleeve (6) at a predetermined actuation pressure (P_(S)).
 15. The transmission shift system according to claim 14, wherein the catch device comprises a ball-spring unit, which comprises a ball (9) that is guided in a bore in the hub element (7), which can be guided into a catch groove (3) of the sliding sleeve (6) by a spring force of a spring element (9), so that the sliding sleeve (6) is blocked in an axial direction.
 16. The transmission shift system according to claim 12, wherein the idler wheel (2) to be shifted is arranged in a frictionally engaged manner for the purpose of adjusting the RPMs between two disk elements (4, 5), wherein a required clamping force for the disk elements (4, 5) can be applied by the actuation pressure that is present on the sliding sleeve (6).
 17. The transmission shift system according to claim 12, wherein an actuating piston (10), which is connected with an oil supply system (12), is provided for the hydraulic actuation of the sliding sleeve (6).
 18. The transmission shift system according to claim 17, wherein the actuating piston (10) can be brought into a starting position by means of a return spring (11).
 19. The transmission shift system according to claim 12, wherein an additional brake plate (13) is provided for the purpose of rotational speed adjustment.
 20. The transmission shift system according to claim 19, wherein the additional brake plate (13) is provided non-rotatably on the shaft (1) between a disk element (5) and the hub element (7).
 21. The transmission shift system according to claim 12, wherein the respective friction surfaces of the disk elements (4, 5) and a brake plate (13) are coated with a suitable material. 